Aromatic carbonates are monomers useful for the preparation of polycarbonates and many studies have been conducted to develop preparation methods thereof. Conventionally, aromatic carbonate esters are prepared by phosgenation of phenol and phosgene in the presence of an alkali. However, this method uses poisonous phosgene and a neutral salt generated as a by-product must be treated.
Accordingly, various attempts have been made to develop a method of preparing an aromatic carbonate ester without phosgene. For example, a method of preparing an aromatic carbonate ester through oxidative carbonylation of an aromatic alcohol with carbon monoxide is known. This method is disadvantageous in that reaction rate and yield are low irrespective of the use of organic metal compounds such as palladium, manganese, cobalt and the like as catalysts; in that there is a risk of explosion due to the use of gas mixture of carbon monoxide and oxygen; and in that the method uses noxious carbon monoxide.
In order to solve such disadvantages, transesterification of phenol and an aliphatic carbonate ester such as dimethyl carbonate to produce an aromatic carbonate ester has been developed. Transesterification is generally conducted in the presence of a catalyst, for example, PbO, TiX4 (X=alkoxy or aryloxy group), SnR2(OPh)2 (R=alkyl group), and the like. However, PbO has high stability but low catalytic activity, causing a significantly low reaction rate. TiX4 and SnR2(OPh)2 have a higher activity than PbO, but have inadequate activity and generate a substantial amount of ether as by-products.
Therefore, there is a need for a method of preparing aromatic carbonate in high yield at low reaction temperature using dialkyl carbonate as a starting material instead of carbon monoxide.